A window will pop up and in the text box will show your main hard disk drive (i.e. C:\). Click the Ok button to run. This may take a little while if you have never run this program before – but be patient – it will complete and your hard drive will love you for it.

You should run this overnight when you are not actively on your computer so it does not get interfered with.

I recommend running this every month as it can speed up your pc and clean up your harddrive.